cmd/keyserver: add insecure hack to allow bootstrapping inprocess key server
cmd/keyserver: add insecure hack to allow bootstrapping inprocess key server

A new flag testuser sets the name of a user whose key will be loaded from the
test keys in the repository. This will allow one to authenticate a connection to
a persistent but inprocess key server, install the keys for a real user, and test
from there.

Enabled only when serving inprocess to locahost.

Change-Id: Id50f32a31bf4f8932d2676c17e45613b6ab8e5e5
Reviewed-on: https://upspin-review.googlesource.com/4262
Reviewed-by: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@google.com>

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